The present invention relates to image sensors, and more particularly, towards the color filters applied to an image sensor.
Image sensors are electronic integrated circuits that can be used to produce still or video images. Solid state image sensors can be either of the charge: coupled device (CCD) type or the complimentary metal oxide semiconductor (CMOS) type. In either type of image sensor, a light gathering pixel is formed in a substrate and arranged in a two-dimensional array. Modern image sensors typically contain millions of pixels to provide a high resolution image. An important part of the image sensor are the color filters and micro-lens structures formed atop of the pixels. The color filters, as the name implies, are operative, in conjunction with signal processing, to provide a color image. The micro-lenses serve to focus the incident light onto the pixels, and thus to improve the fill factor of each pixel.
While the technology underlying the formation of color filters is relatively mature, there are still issues that may arise, particularly at higher integration densities. For example, U.S. Pat. No. 6,297,071, U.S. Pat. No. 6,362,513, and U.S. Pat. No. 6,271,900 show the current state of the color filter art. In most color filter processes, one important requirement is that the color filter layers be applied in a planar manner. This can be made easier if the underlying substrate upon which the color filter is applied is planar to begin with.
The underlying substrate, underneath the color filter layers, is relatively xe2x80x9clumpyxe2x80x9d, due to various reasons. In the prior art, this lumpiness would be simply resolved by first depositing a first planarizing layer using spin on techniques into the valleys of the substrate topography. Then, a second planarizing layer would be deposited over the first planarizing layer. Both planarizing layers are typically polymers, such as polymethylmethylacrylate (PMMA) or polyglycidylmethylacrylate (PGMA). Nevertheless, this approach still does not provide the desired amount of planarization.